1. Field of the Invention
The present invention relates to a buckle for a seat belt that resists unlatching when subjected to rapid acceleration or deceleration.
2. Prior Art
In most juristictions, regulations require that motor vehicles be equipped with seat belts fitted directly or indirectly to the vehicle body at anchorage points in order to secure at least the driver to the driver's seat in the event of accidents. Conventional webbed seat belts include a buckle mechanism wherein one free end of the seat belt has a tongue plate affixed thereto and the opposing free end of the seat belt has a buckle affixed thereto. Examples of such prior art buckle assemblies are described in U.S. Pat. No. 3,851,360 to Minolla, and U.S. Pat. No. 3,969,795 to Stephenson. When the tongue plate is inserted into the main body of the buckle, a latch member housed within the buckle, which is conventionally a spring-loaded pawl, lockingly engages a hole in the tongue plate. The latched state (i.e., locked state) is maintained by a locking member, usually a spring, until the pawl is released from locking engagement with the hole in the tongue plate by manually depressing a release button housed on the buckle. When the locked state of the latch is cancelled by the aforesaid pressing operation of the release button, latch engagement is cancelled and the tongue plate is disengaged from the main body of the buckle.
The above-described type of seat belt buckle is constructed in such a manner that after the tongue plate is fully inserted into the buckle main body to a locked condition, the tongue plate should be reliably held in the locked state even if an impact (i.e., a high G event) is applied to the buckle. The locked condition is maintained because the latch (pawl) is constantly urged (pressed) by a spring member to lockingly engage the hole in the tongue plate. In an automobile, the release button, which is operable for releasing the buckle assembly from the locked state, is structured so as to be able to be pressed by a relatively small force sufficient to overcome the urging force of the spring member and enable disengagement of the tongue plate from the buckle. In aircraft, stronger springs are employed and the release button is activated by a lever that provides the user with the mechanical advantage required to overcome the force of the spring member.
It is important that automobile seat belt buckles do not open unintentionally in the event that a “high G” event such as a crash occurs. When the buckle to which the tongue plate is locked is instantaneously pulled, a condition referred to as “reverse G” occurs in the buckle. In a conventional buckle, even when the release button is not pressed, there is a risk that the tongue plate will disengage from the buckle by the latch being unintentionally cancelled such as may occur when the buckle main body is forcibly and rapidly accelerated or decelerated. When such reverse G conditions occur, an inertial force corresponding to the total mass of the release button and locking mechanism housed within the case of the buckle main body, acts on the release button, locking mechanism and the like in a direction such that the lock state is released. As a result, the lock state may be forcibly cancelled and the tongue plate may release from the buckle main body. In order to prevent the tongue plate from releasing from the main buckle body in the conventional seat belt buckle, the spring force of the spring, which constantly urges the latch to a locked position, may be increased. However, as the spring becomes larger in size, the release force that must be applied to the release button for releasing the locking state of the latch against spring force of the spring, is increased.
Several attempts to address the problem of unintentional release of seat belt buckles during a high G event have been disclosed. Knox, in U.S. Pat. No. 6,918,458, discloses a load management system and method for controlling the activation sequence and times of activation of motor vehicle occupant restraints when a high g event, such as a crash, occurs. The system includes a microprocessor that processes inputs from a number of devices including a seat weight sensor, an occupant spatial position detector, a buckle status detector and a belt sensor. The microprocessor is driven by a load management procedure that includes a high G event routine that controls the activation sequence of restraints so that the automatic locking restraint is first activated, followed by the pre-tensioner and then by the air bag. The load management procedure also includes an enable/disable procedure that controls the enabling and disabling of the restraints according to a number of variables including occupant weight, seat buckle status and belt extension status.
Katsuyama et al., in U.S. Pat. No. 6,588,077, disclose a seat belt buckle which is operable for preventing the ejection of a tongue plate from a buckle main body under reverse G conditions without increasing release force for releasing a lock state. In accordance with the teaching of Katsuyama et al., the seat belt buckle comprises a latch including a latch swinging end portion, a lock member including a lock swinging end portion, which is made to swing between a lock position, at which at the time of latching, the lock swinging end portion swings on the latch swinging end portion and (sic) engage to stop the latch swinging end portion in a state of pressing the latch swinging end portion toward engagement holes of a tongue plate and a base while pressing the same in a tongue plate insertion direction, thereby locking the latching, and a lock release position, a lock operation end portion for releasing the locking and a weight portion formed at the side of the lock swinging end portion.
In view of the complexity of the above-referenced prior art solutions, there remains a continuing need for a seat belt buckle that has simple construction and resists disengagement when subjected to a high G event. A simple solution to the problem of unintentional release of a seat belt during crash impact has been disclosed by Renzi, Sr. et al. in U.S. Pat. No. 5,416,957. Renzi, Sr. et al. disclose an impact cushion for a seat belt latch comprising a sleeve of a latex rubber material sized to slide lengthwise over a female seat belt connector with an interference fit. The front side of the sleeve has an opening in a position corresponding to the release button of the connector, so that the button is not obstructed. The rear of the cushion is provided with a rigid metal plate; segmented ribs running lengthwise along the inside upper and lower surfaces of the sleeve hold the rear of the seat belt a short distance away from the plate. The cushion is intended to reduce the incidence of seat belt buckle failure during accidents, resulting from impact directly to the buckle. The impact cushion is not effective for preventing the unintentional release of the tongue blade from the buckle unless the impact is delivered directly to the buckle. There remains a need for a seat belt buckle that resists unintentional release of the tongue blade when the buckle is subjected to a high G event even when the buckle is not directly impacted.